Fix for Mantis #24687.

pgenutil.pas:
  + add new function could_be_generic which checks whether a given symbol name could be a generic (which is determined using the genericdummysyms list for the current module)
pexpr.pas:
  * factor: only do a typecheck pass (postfixoperators does one as well) if the found node can not be a generic type
  * sub_expr: do a typecheck pass if it isn't a specialization

+ added test


git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@25579 3ad0048d-3df7-0310-abae-a5850022a9f2